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Compressor Size Guide

The first questions to ask yourself are:

  • What electricity supply is available at your premises? (single or three phase)
  • Do you currently have a compressor?
  • If so, what size compressor is it? Does it cope ok with the current demand on it?
  • What are the future plans? More staff and tools?


Electrical Supply

Single Phase (Domestic) 230 Volts

Standard 13 Amp plug
Note: Do not use long extension cables when running the compressor! Better to use a long air hose.

Here are all the compressors available that run off a 13 Amp plug:

Workshop range:

http://www.airsupplies.co.uk/air-compressors/garage-diy-air-compressors.html

Semi Pro range

http://www.airsupplies.co.uk/air-compressors/workshop-semi-professional-air-compressors.html

The biggest compressor you can get that runs off a 13 Amp plug is the ABAC A29B 150 FM3

http://www.airsupplies.co.uk/abac-a29b-150-fm3-belt-driven-air-compressor-3-hp-150-litre-11-2-cfm-single-or-three-phase.html

And this is the largest portable one:

http://www.airsupplies.co.uk/abac-pro-a29b-90-cm3-b312-100-belt-drive-air-compressor-3hp-90-litre-14-cfm.html

 

Single phase (Professional) 230 Volts

Any single phase compressor bigger than 3hp on a 150 litre air receiver will require a minimum of 20 Amps supply, with type D breakers. This is because of the draw on the starter motor. 

These are all the single phase 20 amp compressors available:

http://www.airsupplies.co.uk/air-compressors/professional-industrial-compressors.html

The biggest compressor you can get is the ABAC A29B 150 FM3

http://www.airsupplies.co.uk/abac-b3915-200-pro-a39b-200-fm3-belt-driven-air-compressor-3-hp-200-litre-14-cfm-single-or-three-phase.html

Main Benefit of Single Phase
• Excellent second-hand resale value

 

Three phase (Professional) 400 Volts

See them all here. 

http://www.airsupplies.co.uk/air-compressors/professional-industrial-compressors.html

Main Benefit of Three Phase
• Approx 2/3 cost saving over single phase
• Stable supply
• Longer motor life

 

Single vs Three phase

Three-phase compressors are more efficient producers of compressed air than single-phase equivalent units, so where a three-phase supply is available the best option is the three-phase compressor.

 

110 Volts

For on site / portable use. 

There are limited compressors available running off 110 Volts.

See them all here:

http://www.airsupplies.co.uk/air-compressors/110-volt-air-compressors.html

 

Air Tools CFM Table


Bodyshop

Using the air tools CFM table, add all the tools CFM together and divide by two. The result figure is the minimum free air you require.


Workshop

Using the air tools CFM table, add all the tools CFM together and divide by three. The result figure is the minimum free air you require.


Quick guide to CFM/FAD output (approx) of existing compressor
Multiply motor hp by 3.3 = output in CFM / FAD
Multiply motor kW by 4.5 = output in CFM / FAD
Multiply motor kW by 2.1 = output in L/sec / FAD

 

Using the table

If its tools, please tick the tool with the highest continuous use CFM requirement. So if you are planning on use say an 3/8” impact wrench, a ¼” drill and sometimes a belt sander, then pick the sander as your highest CFM tool at 27 CFM

 

Air Tool CFM Table

Tool Type

Continuous use CFM used (approx.)

50% CFM Average Use (30 Seconds)

25% CFM Average Use (15 Seconds)

¼” Drill

15

7.5

3.75

5/16” Drill

18

9

4.5

3/8” Drill

18

9

4.5

½” Drill

20

10

5

¼” Ratchet

14

7

3.5

3/8” Ratchet

18

9

4.5

½” Ratchet

18

9

4.5

3/8” Impact Wrench

12

6

3

½” Impact Wrench

21

10.5

5.25

¾” Impact Wrench

38

19

9.5

1” Impact Wrench

70

35

17.5

¼” Impact Wrench

15

7.5

3.75

5/16” Impact Wrench

16

8

4

Flat Bed Orbital Sander

20

10

5

5” Random Orbital (DA) Sander

15

7.5

3.75

6” Random Orbital (DA) Sander

22

11

5.5

5” High Speed Sander

23

11.5

5.75

7” Angle Sander

23

11.5

5.75

Belt Sander

27

13.5

6.75

3mm (1/8”) Die Grinder

7

3.5

1.75

6mm (1/4”) Die Grinder

17

8.5

4.25

4” Angle Grinder

19

9.5

4.75

5” Angle Grinder

38

19

9.5

7” Angle Grinder

42

21

10.5

Straight Ling Polisher

19

9.5

4.75

8” Angle Polisher

27

13.5

6.75

Blowgun

25

12.5

6.25

Fibreglass Saw

19

9.5

4.75

Reciprocating Saw

12

6

3

Chisel Gun

12

6

3

Riverter

7

3.5

1.75

Upholstery Tacker

3

1.5

0.75

Coil Nailer

7

3.5

1.75

Spray Gun Normal

8

4

2

Spray Gun HVLP

14

7

3.5

 

How many people will be using tools at one time? 

If its just you using the tools.

Multiply the highest CFM by 1.2. This is to over compensate the CFM required. 

 

If its 2 people, then multiply the CFM required by 1.7. 

Note: Small average low use. 

This is not continuous use. This is average interminant use.

 

If the CFM figure is bigger than 50 CFM then you will need a screw compressor. The highest direct drive compressor you can get is 20 CFM and the highest CFM from a belt driven is the twin at 34 CFM delivered.

If you are going to use the compressor for continuous use or any more than 2 people using tools at one time, then you need to be looking at screw compressors. Available with or without receivers, dryers and filters.

 

Disclaimer
Please note, this is only a guide and should not be treated as anything other than a guide. 
Call us if you are not sure.

 

Definitions

Pressure
Pressure is the force of the compressed air.

Measured in PSI (Pounds per Square Inch) or Bar.

If the pressure is too low then this will cause the tools to not work. If the pressure is too high then this could put unnecessary wear on the tools.

 

Displacement (Volume)
This is the theoretical volume produced by the compressor

The measured by the swept volume of a cylinder multiplied by the number of compressions in a minute. Expressed in CFM (Cubic Feet per Minute).

The CFM (Displacement) should not be used in calculating the size of compressor you require. Because it is theoretical, it does not represent the actual CFM delivered after heat and friction losses in the compressor system.

 

Free Air Delivered
Remember displacement is the theory and CFM (Free Air Delivered) is the actual volume delivered.

For calculation purposes always use free air delivered figures.


Single Stage / Two Stage Compressors

Single Stage Compressors
One or more cylinders producing the final pressure in one compression.
Normal maximum pressure 150 psi. g.

Two Stage Compressors
Air is compressed in the first stage, cooled then compressed to final pressure in the second stage. Normal maximum pressure 200 psi. g.

Two stage provides more air for less energy.

2 Stage compressors start here: http://www.airsupplies.co.uk/abac-pro-5900b-200-ft5-5-b5924-200-belt-driven-air-compressor-5-5-hp-200-litre-23-cfm-three-phase.html


Compressed Air Hose Guide

¼” (6mm)

Upholstery tacking gun, Tyre inflator, Airburshung, Blow gun

 

5/16” (8mm)

Spray guns, 18 gauge pinner, brad nailer, 3/8” drill, ratchet wrench, small die grinders


3/8”

HVLP/LVLP Spray Guns /

½” impact wrench, sanders, 4” grinders,


1/2”

1” and 3/8” Impact Wrenches

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